Institute of Microwaves and Photonics
SCHOOL OF ELECTRONIC AND ELECTRICAL ENGINEERING,
FACULTY OF ENGINEERING
A low cost upper atmosphere sounder
(LOCUS) mission
Edmund Linfield, Giles Davies, Paul Dean, John Plane
University of Leeds
Brian Ellison, Martin Crook, Tom Bradshaw, Bruce Swinyard (also UCL),
Daniel Gerber
RAL Space
Steve Parkes (Star Dundee)
Funded by CEOI 7th EO Technology Call
So what is LOCUS?
A breakthrough concept multi-terahertz remote sounder
Compact payload to be flown on a
‘standard’ small satellite that will:
• Measure key species in the upper
atmosphere, i.e. the mesosphere and
lower thermosphere (MLT);
• Increase understanding of natural and
anthropogenic effect on climate
change;
• Allow study of the ‘gateway’ between
the Earth’s atmosphere and near space
environment.
Small satellite sounder from LEO
Why use terahertz sounding?
• Terahertz (THz) frequencies (sub-mm-waves) penetrate dielectric
media opaque at most other shorter wavelengths;
• Can detect and characterize molecular species through obscurants
and located in a relatively low temperature environment;
• Offers higher spatial resolution than microwave/mm-wave range;
• Allows remote sounding of atmospheric constituents related to
climate change on a local or global basis;
• Same technique provides information on the interstellar media, e.g.
regions of star formation.
What science will be investigated?
LOCUS science achieved through:
• Tracing O, OH, NO, CO, O3, H2O, HO2,
O2 spectral emission signatures
globally and from low Earth orbit
(LEO);
• Using a limb sounding technique
with cold space as a background to
achieve height distribution;
• Provision of ultra-high spectral
resolution (1MHz);
• Accurate spatial sampling with ~2km
footprint at tangent heights from ~
55km to 150km.
Species
O
OH
But, this requires terahertz instrumentation:
HO2
NO
CO
O2
Transition Frequency (THz)
4.745
3.544
3.543
3.544
1.153
1.153
1.152
0.773
And therein lies one challenge…
IMPATT – Impact Ionization
Avalanche Transit-Time
diode
HG – Harmonic Generation
RTD – Resonant-Tunnelling
Diode
TPO – THz Parametric
Oscillator
PCS – Photoconductive
Switch
QCL – Quantum Cascade
Laser
M. Tonouchi, Nature Photonics, 1, 97 (2007)
LOCUS Instrumentation
To be based on heterodyne receiver technology, which converts THz
input signal to a lower intermediate frequency (IF) – typically GHz;
Provides low noise and high spectral resolving power - order >>104;
Key front-end components are the mixer and THz local oscillator (LO).
The heterodyne approach
Optimum system
performance requires:
o Efficient signal frequency
translation, i.e. low
conversion loss;
o Minimal added system
electrical noise;
o Provision of adequate THz
LO source power.
e.g. RAL & STAR Dundee 350GHz
Heterodyne Radiometer (previous
CEOI funding)
The LOCUS payload concept
Key features:
• Highly integrated multi-channel THz radiometer system;
• Four separate bands identified that accommodate the
required spectral windows;
• Schottky semiconductor diode mixer technology;
• Quantum Cascade Laser used a LOs for 1 and 2,
harmonic up-conversion for 3 and 4;
• Fast Fourier Transform digital spectrometers provide
1MHz spectral resolution;
• Single primary ~ 40cm diameter and miniature coolers –
100K operational goal;
• UK sourced technology with critical elements support
by the CEOI and NERC.
Electronic behaviour
2 QCLs
Peak performance corresponds to efficient injection of current
Device dimensions are typically 1 mm × 150 μm × 10 μm
Quantum Cascade Lasers (2)
• Precise frequencies can be
defined using periodic
gratings defined into the
ridge waveguides;
1.5
10 K
20 K
30 K
40 K
50 K
60 K
70 K
80 K
90 K
100 K
110 K
118 K
18
Voltage (V)
• QCLs have an intrinsically
narrow linewidth (<20 kHz);
24
12
• Radiation hardness has
been demonstrated.
HR
1.0
0.5
6
x40
0.0
0
0
• Operation has been
demonstrated over the
1 – 5 THz frequencies;
425 um x 4.2 mm
Power (W)
• 1 W peak power is possible,
and 10s of mW continuouswave power, but cooled;
200
400
600
800
2
Current density (A/cm )
2% duty cycle; ;asing up to 1.01 W (peak) at
~ 3.4 THz; > 400 µW at 77 K, Tmax = 118 K:
L. Li et al, Electronics Letters 50, 309
(2014).
LOCUS Core Technology
Schottky Barrier Diode
& Space Coolers RAL
QCL Local Oscillator
University of Leeds
Digital Spectrometer
STAR-Dundee
UK also leading LOCUS science definition via
Leeds, UCL and RAL
Small Satellite
Surrey Satellites Ltd
In-orbit demonstration
– satellite concept
Objective: Prove core payload and platform
technology in space:
• Polar sun synchronous orbit;
• Perform global species measurement;
• Novel approach to scene scanning via spacecraft
nodding;
• Cold-space view and on-board c300K target
provide payload calibration;
• Approx. total spacecraft volume, mass & power:
1m3, 150kg, 70W.
o Compare with NASA AURA @ 43m3, 3tonne, 4kW
& MLS: ~8m3, 500kg, 550W);
• IOD mission lifetime ~ 2 years, tbc.
Mission Concept Development Plan
Funding (with thanks)
ESA In-orbit Demonstration Study Programme (SSTL PI):
• Science refinement;
• Payload concept definition;
• Spacecraft concept definition;
• Mission plan and cost estimate.
NERC Critical Component Development (RAL PI):
• QCL development and waveguide demonstration;
• THz Schottky diode development;
• Integrated QCL & Schottky proof of concept.
CEOI-ST Critical Payload Development (Leeds PI):
• 1.1 THz (Band 3) full development including:
o Mixer, LO and spectrometer;
• QCL frequency stabilisation.
Summary
• THz remote sounding provides important information in relation
to the Earth’s climate evolution and its monitoring;
• The THz detection method depends upon the nature of the
defined science return;
• Where the science requires high spectral resolution and high
sensitivity, THz heterodyne detection is the instrumentation of
choice;
• In the 1 to 5 THz frequency range, novel heterodyne
instrumentation is being conceived and developed that will allow
novel scientific study;
• A UK initiated and presently majority UK funded instrument,
LOCUS, is being developed to study the relatively unexplored
supra-THz spectral range.
The LOCUS Team Members
Thank you for your attention